• Title/Summary/Keyword: Elliptic cylinder

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A numerical study of the effect of the aspect ratio of elliptic cylinder on the aerodynamic force (변장비 변화가 타원형 실린더에 작용하는 유체력에 대한 영향 연구)

  • Im, Jun-U;Im, Sang-Muk;Kim, Wan-Seop;Kim, Hyeon-U;Lee, Seung-Su
    • Proceeding of EDISON Challenge
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    • 2012.04a
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    • pp.73-76
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    • 2012
  • 변장비의 변화에 따른 타원형 실린더 주위의 유동장을 해석하기 위하여 Navier-Stokes 방정식을 사용한 EDISON 열유체 툴로 분석하였다. 본 논문은 기존의 연구와 비교 분석하는데 목적을 두었으며, 기존의 연구결과와 비교 분석하기 위하여 계산 영역을 동일하게 설정하였다. 타원형 실린더의 변장비를 0.5, 1, 2, 4로 변화시키고 레이놀즈수 200, 400, 1000인 조건하에 유동장을 해석하였다. 본 연구의 해석 결과를 통해 선행연구와 전체적인 경향이 같다는 것을 알 수 있었고, 또한 변장비와 레이놀즈수는 항력진폭과 양력진폭, 스트로할 수에 영향을 미침을 알 수 있었다.

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Microwave Incoherent Imaging of a Conducting Cylinder by using Multi-Frequency Time-Harmonic Field : Part II - Microwave Incoherent Imaging of a Conducting Cylinder (다중주파수 시간조화신호를 사용한 도체기둥의 초고주파 incoherent 영상 : Part II - 도체기둥의 초고주파 incohernet 영상)

  • 강진섭;라정웅
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.33B no.2
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    • pp.56-64
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    • 1996
  • In the previous paper of this study, an incoherent intensity pattern of a conducting cylinder is obtained by averaging out the multi-frequency intensities of the time-harmonic fields scattered from this cylinder. in this paper, an incoherent imaging of a conducting cylinder is obtained via the back-projection of the incoherent intensity patterns calculated from the circular rotational measurement configuration. This imaging method is vlaidated by imaging a conducting circular and a conducting elliptic cylinder and the measurement conditions to get better image are investigated.

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The effects of axis ratio and rotation angle on flows around an elliptical cylinder (타원의 장단축 비율과 회전 각도에 의한 유동 변화)

  • O, Geun-U
    • Proceeding of EDISON Challenge
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    • 2014.03a
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    • pp.619-624
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    • 2014
  • 본 논문에서는 타원형 실린더 주위의 유동과 항력 및 양력 계수의 변화를 관찰하였다. EDISON_CFD를 이용하여 자유 유동(free stream)에서 타원형 실린더의 장단축 비율과 회전된 각도의 변화에 따라 실린더 후방의 유동과 압력 분포의 변화를 보고, 이에 따른 항력 계수 및 양력 계수의 변화를 시뮬레이션 하였다. 또한, 채널 유동 내에서 벽 근접에 따른 유동 변화와 항력 및 양력 계수의 변화를 관찰하였다.

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An Analysis of Electromagnetic Wave Scattering for the Elliptic-Multi Layer Dielectric Cylinders (다층타원 유전체주의 전자파 산란 해석)

  • 박동희;김정기
    • The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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    • v.2 no.3
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    • pp.26-31
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    • 1991
  • The scattering property of TMz illuminated a elliptic dielectric cylinders with arbitrary cross section are analyzed by the boundary element techniques. The boundary element equations are for- mulated via Maxwell's equations, weighted residual of Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by the boundary element integral equations. Once the surface fields are found, the scattered fields in far-zone and scattering widths (SW) are readily determined. To show the validity and usefulness of this formulation, computations are compared with those obtained using analytical method and one layer circular cylinder. As exten- sion to arbitrary cross-sectioned cylinders, plane wave scattering from a elliptic dielectric cylinders are numerically analyzed. A general computer program has been developed using the quadratic ele- ments(Higher order borndary elements) and the Gaussian quadrature.

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NUMERICAL STUDY ON COMBINED HEAT TRANSFER IN NIR HEATING CHAMBER (근적외선 열풍기의 복합열전달에 관한 수치적 연구)

  • Choi, H.K.;Yoo, G.J.;Kim, I.H.
    • Journal of computational fluids engineering
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    • v.12 no.4
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    • pp.7-13
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    • 2007
  • Numerical analysis is carried out for combined heat transfer in an indirected NIR(Near Infrared Ray) heating chamber. Reynolds number and shapes of absorbed cylinder are known as important parameters on the combined heat transfer effects. Reynolds number based on the outer diameter of the cylinder is varied from $10^3$ to $3{\times}10^5$. Four difference heat transfer regimes are observed: forced convection and radiative heat transfer on the outer surface of the cylinder, pure conduction in the cylinder body, pure natural convection and radiation between lamp surface and inner surface of the cylinder, and radiation from the lamp. Flow and temperature characteristics are presented with iso-contour lines for the absorbed circular and elliptic cylinders to compare their differences. The convective and radiative heat transfer fluxes are also compared with different Reynolds numbers. As usual, Reynolds number is an important factor to estimate increasing convective heat transfer as it increases. The shape of absorbed cylinder results overall heat transfer rates remain unchanged.

A Numerical Study on the Effect of the Cylinder Shape Modification on the Forced Convection Around a Circular Cylinder (실린더 형상 변화가 실린더 주위 강제대류에 미치는 영향에 관한 수치적 연구)

  • Kim, Min-Ho;Ha, Man-Yeong;Yoon, Hyun-Sik;Lee, Jin-Wook
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.10
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    • pp.670-677
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    • 2011
  • Direct numerical simulation are performed in order to investigate the effect of the circular cylinder shape on the forced convection around a circular cylinder at the Reynolds number of 300 and Prandtl number of 0.71. Three-dimensional characteristics of fluid flow and heat transfer around the smooth, wavy and torsional cylinders are investigated. A wavy cylinder has the sinusoidal variation in the cross sectional area along the spanwise direction with the wave length of ${\pi}/3$ and wavy amplitude of 0.1. A torsional cylinder has the twisted elliptic cross section with a torsional period of ${\pi}/2$ and an axis ratio of 1.35 corresponding to the major axis of 1.15 and the minor axis of 0.85. The value of time-and surface-averaged drag coefficient for the smooth cylinder is similar to that for the wavy cylinder, but larger than that for the torsional cylinder. The time and surface-averaged lift coefficient for the smooth cylinder is larger than that for the wavy and torsional cylinders. The time-averaged local heat transfer rate for the wavy and torsional cylinders shows different distribution along the circumferential direction, compared to that for the smooth cylinder because of the shape change in the spanwise direction for the cases of the wavy and torsional cylinders.

Large Eddy Simulation of Flow around Twisted Offshore Structure with Drag Reduction and Vortex Suppression (와류감쇠 및 저항저감형 나선형 해양 구조물 주위 유동 LES 해석)

  • Jung, Jae-Hwan;Yoon, Hyun-Sik;Choi, Chang-Young;Chun, Ho-Hwan;Park, Dong-Woo
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.5
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    • pp.440-446
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    • 2012
  • A twisted cylinder has been newly designed by rotating the elliptic cross section along the spanwise direction in order to reduce the drag and vorticies in wake region. The flow around the twisted cylinder at a subcritical Reynolds number (Re) of 3000 is investigated to analyze the effect of twisted spiral pattern on the drag reduction and vortex suppression using large eddy simulation (LES). The instantaneous wake structures of the twisted cylinder are compared with those of a circular and a wavy cylinder at the same Re. The shear layer of the twisted cylinder covering the recirculation region is more elongated than that of the circular and the wavy cylinder. Successively, vortex shedding of the twisted cylinder is considerably suppressed, compared with those of the circular and the wavy cylinder. Consequently, the mean drag coefficient and the fluctuating lift of the twisted cylinder are less than those of the circular and the wavy cylinder.

An experimental study on natural convection in the annuli between two horizontal elliptic cylinders (수평타원 환상공간에서의 자연대류에 관한 실험적 연구)

  • 이재순;서정일;이택식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.1
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    • pp.28-35
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    • 1988
  • Experimental study has been carried out on natural convection in the annuli formed by two isothermal horizontal inner and outer elliptic cylinders with uniform gap. The eccentricities of inner and outer elliptic cylinder and the gap ratio for the experimental model were 0.5078, 0.389 and 0.363 respectively. The temperature distributions were obtained through the analysis of interferograms which were taken by Mach-Zehnder interferometer in the range of Rayleigh number (Ra$_{L}$) from 0.34*10$^{4}$ to 3.07*10$^{4}$. It showed that flow was laminar when Ra$_{L}$.leg. 2.5 *10$^{4}$, while above the range of Rayleigh number we could get information on the fluctuation of interference fringe. Therefore, the upper limit of Ra$_{L}$ for the correlation equation of mean equivalent conductivity in reference(1) is confirmed. The flow pattern could be visualized by simple smoke test. The comparison of streamlines, isotherms, temperature distributions and local equivalent heat conductivity between existing numerical and present experimental results showed good agreement.ement.

THE EXPONENTIAL GROWTH AND DECAY PROPERTIES FOR SOLUTIONS TO ELLIPTIC EQUATIONS IN UNBOUNDED CYLINDERS

  • Wang, Lidan;Wang, Lihe;Zhou, Chunqin
    • Journal of the Korean Mathematical Society
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    • v.57 no.6
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    • pp.1573-1590
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    • 2020
  • In this paper, we classify all solutions bounded from below to uniformly elliptic equations of second order in the form of Lu(x) = aij(x)Diju(x) + bi(x)Diu(x) + c(x)u(x) = f(x) or Lu(x) = Di(aij(x)Dju(x)) + bi(x)Diu(x) + c(x)u(x) = f(x) in unbounded cylinders. After establishing that the Aleksandrov maximum principle and boundary Harnack inequality hold for bounded solutions, we show that all solutions bounded from below are linear combinations of solutions, which are sums of two special solutions that exponential growth at one end and exponential decay at the another end, and a bounded solution that corresponds to the inhomogeneous term f of the equation.